Self-organization of multiple shear bands in CoCrNi chemically complex medium entropy alloys

Complex concentrated alloys (CCAs), also known as medium/high entropy alloys (M/HEAs), possess a multitude of outstanding properties attributing to their distinctive chemically disordered structure, which endows them with broad application prospects in many engineering fields. As a fundamental and ubiquitous non-equilibrium phenomenon, shear localization has received significant attention during past several decades. However, the collective behavior of multiple shear bands in CCAs or M/HEAs has not been comprehensively elucidated. Here, we tackle this problem in CoCrNi medium entropy alloy by thick-walled cylinders technology. Via the experimental design, the specimens subjected to diverse deformations were effectively "frozen", thereby facilitating the acquisition of the self-organization characteristics of multiple shear bands in distinct evolution stages. A notable scaling law of multiple shear band spacing was identified. To uncover the underlying physical mechanism of the scaling law, a multiple shear band energy dissipation evolution dynamics model was formulated. Subsequently, a competing map of shear band nucleation and growth was established. It is found that the coordinated propagation of stacking faults and twins may trigger the transformation from the face-centered cubic structure to the hexagonal close-packed structure and even amorphization in late stage of shear band growth. The amorphization regions possess a high probability of serving as nucleation sites with a propensity for void formation. Eventually, with the progression of void evolution, fracture occurs.